Hi,
You need to separate the birds immediately before the male kills the other birds. Budgies can kill another budgie very quickly. When you introduce new birds, it has to be done gradually because they are not necessarily going to get along. They need to be put in a cage next to the other cage until you see signs that they might be interested in each other. Also, your cage really isn’t large enough for two pairs. They each want their own space. Your cage size is about the right size for a single pair, especially if you ever plan to breed them.
As for the two new birds, I don’t think they should be together right now. A young hen should not be paired with a mature male. He will get frustrated with her because she isn’t ready to breed, and he will attack her and in some cases kill her. Since he is already attacking her, she is in danger. You need to remove the new birds, and put them in 2 different cages. If you can’t do this, then you may need to return them to the pet store. As for the original pair, they don’t need more birds in the cage. They are still settling in and are not bored, they just aren’t used to their home yet. Budgies love toys so I would get them some fun toys and let them continue to settle into your home.
Thank you for asking Lafeber,
Brenda